The invention relates generally to the field of circuits in which a signal is provided which varies in a known manner in accordance with a sensed variable. More particularly, the present invention relates to a percentage error reduction circuit which has been used with a pressure sensor input signal representative of sensed pressure to provide an output signal having less percentage error as a function of sensed pressure.
Generally, prior sensor circuits sense a variable and produce an electrical signal having a magnitude representative of the sensed variable. Typically, this electrical signal is temperature compensated so as to minimize undesired temperature variations which may occur in either the sensor itself or the subsequent circuitry which processes the output of the sensor. Generally, it is desired to have the output signal vary linearly as a function of the sensed variable, and some prior sensor circuits have been able to implement such a relationship. However, when such prior circuits have been successful in providing a substantially linear variation of the output signal as a function of the sensed variable over a substantial range of magnitude of the sensed variable, this means that the percentage of error, or uncertainty with regard to the magnitudes of the sensed variable, is relatively high at the lower range of the sensed variable as compared to the upper range of the sensed variable. This is because the percentage of error is a function of the magnitude of the sensed variable and therefore automatically decreases as the absolute value of the sensed variable increases. Thus even though some prior circuits have been successful in providing an output signal that varies substantially linearly as a function of a sensed variable over a substantial range of variable magnitudes, the circuits produce the undesirable result of having a relatively large percentage of error at the lower portion of the range of the sensed variable as compared to a much smaller percentage of error at the higher range of the sensed variable.
Some prior circuits for processing a sensor signal have provided an output signal which varies differently with regard to the sensed variable for different ranges of the sensed variable. Typically such circuits are implemented by utilizing circuitry in which the break point between each rate change for the output signal is determined by the turn on threshold of a semiconductor device, such as a diode, which threshold is substantially temperature dependent. Such circuits are therefore inherently inaccurate or have to utilize extensive temperature compensation circuits to achieve any degree of accuracy since the occurrence of the rate change break points are very susceptible to temperature variations. Also, typically the circuitry utilized to implement prior rate change break points resulted in any change in the break point also substantially affecting the magnitude of the rate to be implemented. Thus these prior circuits required a number of iterative adjustments to achieve a final desired result since any break point adjustment also then required a rate magnitude adjustment.